engleski

Apoptosis in FADD knockout cells resistant to TNF

Photodynamic therapy (PDT) with phthalocyanine 4 (Pc4) is an oxidative stress that generates cytotoxic damage and rapid induction of apoptosis. It also induced increased intracellular tumor necrosis factor (TNF), multifunctional cytocine that mediates apoptosis downstream from CD95 receptor complex. FADD (Fas associated death domain) protein is the signal transducer downstream of this receptor complex. To assess the role of FADD, in apoptosis induced by PC4-PDT, embryonic fibroblasts derived from FADD knock out 8k/o) and wild type mice were used. Pc4-PDT induced casp-3 activation and apoptosis was abrogated in both cells line. Surprisingly, induced ceramide generation was inhibited or remained unchanged after co-treatment with Pc4-PDT and zVADfmk in FADD k/o and FADD wt cells, respectively. Fumonisin B1 (FB), an inhibitor of ceramide synthase, had no effect on apoptosis after Pc4-PDT in either cell line. In contrast to Pc4 photosensitization, TNF did not induce either apoptosis or ceramide accumulation in FADD k/o cells. In the absence of FADD deficiency, TNF-induced apoptosis was FB-insensitive and zVADfmk-sensitive. Induced ceramide levels remained elevated after co-treatment with TNF and zVADfmk in FADDwt cells. This suggest that Pc4-PDT induced apoptosis is FADD-independent. FADD signalling resides upstream of ceramide action and is not indispensable for oxidative stress induced apoptosis.

apoptosis; tumor necrosis factor; photosensitization; phthalocyanine 4; FAS associated death domain

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